| Message ID | 20180308022756.GA28733@embeddedor.com |
|---|---|
| State | Accepted |
| Headers | show |
| Series | [v2] rtc: remove VLA usage | expand |
On 07/03/2018 at 20:27:56 -0600, Gustavo A. R. Silva wrote: > In preparation to enabling -Wvla, remove VLA and replace it > with a fixed-length array instead. > > From a security viewpoint, the use of Variable Length Arrays can be > a vector for stack overflow attacks. Also, in general, as the code > evolves it is easy to lose track of how big a VLA can get. Thus, we > can end up having segfaults that are hard to debug. > > Also, fixed as part of the directive to remove all VLAs from > the kernel: https://lkml.org/lkml/2018/3/7/621 > That is a good description, thanks > Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com> > --- > Changes in v2: > - Update changelog as per Alexandre Belloni request. > - Update the code for rtc-bq32k driver based on Alexandre's feedback. > > drivers/rtc/rtc-bq32k.c | 6 +++++- > drivers/rtc/rtc-mcp795.c | 2 +- > 2 files changed, 6 insertions(+), 2 deletions(-) > Applied.
diff --git a/drivers/rtc/rtc-bq32k.c b/drivers/rtc/rtc-bq32k.c index e8698e9..ef52741 100644 --- a/drivers/rtc/rtc-bq32k.c +++ b/drivers/rtc/rtc-bq32k.c @@ -36,6 +36,10 @@ #define BQ32K_CFG2 0x09 /* Trickle charger control */ #define BQ32K_TCFE BIT(6) /* Trickle charge FET bypass */ +#define MAX_LEN 10 /* Maximum number of consecutive + * register for this particular RTC. + */ + struct bq32k_regs { uint8_t seconds; uint8_t minutes; @@ -74,7 +78,7 @@ static int bq32k_read(struct device *dev, void *data, uint8_t off, uint8_t len) static int bq32k_write(struct device *dev, void *data, uint8_t off, uint8_t len) { struct i2c_client *client = to_i2c_client(dev); - uint8_t buffer[len + 1]; + uint8_t buffer[MAX_LEN + 1]; buffer[0] = off; memcpy(&buffer[1], data, len); diff --git a/drivers/rtc/rtc-mcp795.c b/drivers/rtc/rtc-mcp795.c index 79e24ea..00e11c1 100644 --- a/drivers/rtc/rtc-mcp795.c +++ b/drivers/rtc/rtc-mcp795.c @@ -82,7 +82,7 @@ static int mcp795_rtcc_write(struct device *dev, u8 addr, u8 *data, u8 count) { struct spi_device *spi = to_spi_device(dev); int ret; - u8 tx[2 + count]; + u8 tx[257]; tx[0] = MCP795_WRITE; tx[1] = addr;
In preparation to enabling -Wvla, remove VLA and replace it with a fixed-length array instead. From a security viewpoint, the use of Variable Length Arrays can be a vector for stack overflow attacks. Also, in general, as the code evolves it is easy to lose track of how big a VLA can get. Thus, we can end up having segfaults that are hard to debug. Also, fixed as part of the directive to remove all VLAs from the kernel: https://lkml.org/lkml/2018/3/7/621 Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com> --- Changes in v2: - Update changelog as per Alexandre Belloni request. - Update the code for rtc-bq32k driver based on Alexandre's feedback. drivers/rtc/rtc-bq32k.c | 6 +++++- drivers/rtc/rtc-mcp795.c | 2 +- 2 files changed, 6 insertions(+), 2 deletions(-)